1. Field of the Invention
The present invention relates to the field of linear actuators with permanent magnet, which in general is thin. Such linear actuators comprise a stator structure having two poles excited by an electric coil, plus a moving part provided with a yoke and a magnetized portion.
2. Discussion of the Background
The general principle of such actuators is described in French Patent FR 97/10585.
Such actuators employ a magnetic structure comprising three thin magnets magnetized in alternating directions.
A first disadvantage of the prior art actuators is the need for three permanent magnets. High-performance magnets are relatively expensive, and for this reason the prior art structures have a high manufacturing cost.
A second disadvantage is related to the fact that the alternation of polarity of the thin magnets makes it necessary to magnetize the magnets before assembly, and thereafter to bond the three magnets adhesively to the yoke.
A third disadvantage of the prior art actuators results from the fact that the magnetostatic force produced by the architecture of these actuators tends to pull the moving portion backward strongly in the middle of its travel, thus causing problems for certain applications.